Humus Status of Arable Podzoluvisols and the Role of Annual Litterfall in its Formation

Abstract

AbstractIn this work comparative research of the quantitative characteristics of the humus status (HS) of Estonian arable Podzoluvisols (PD) and some very closely related soils were carried out. This study was conducted to determine soil humus cover (HC) and subsoil humus content (percentage and pool) and to analyse the role of plant residues in their formation. The specific objective was to discuss the ecological factors and mechanisms which influence the flux of soil organic matter (SOM) through soils and to evaluate its contemporary status. For this purpose different databases (DB) were used: (1) DB of large‐scale soil mapping (1958‐78), (2) DB PEDON of pedoecological researches (1967‐85), (3) DB of HS research transects (1986‐91) and (4) data from two long‐term field trials (1985‐92). In the conditions of regular agricultural practice the mean SOM percentage in the HC of arable PD is within the range of 1.8‐2.1 %, which is 0.1‐0.3 units (%) the below optimal level and is in a critical state. Impoverishment is caused mainly by deep plowing. The dependence of humus retaining capacity (presumed to be a good criterion for evaluating the current HS of soils) on the mode and intensity of tillage, soil water regime, carbonate content and textural class was discussed. Mean annual inflow of organic matter into HC (4‐5 Mg ha‐yr−1) forms an average 5.5‐6.7 % from its pool in soil. Application of manures increases this percentage to 12‐13. It may be concluded that the HC might be shallower, but must be richer in humus. The annual balance of SOM reflects better than annual balance of humus, the influence of fresh SOM on the soil current year productivity.